BO Union of Data or Join of Data

BO Experts:

My question can be very dumb as I do not know much about BO.

1) In SAP BW Multi-Provider is Union of data

2) Infoset is DataBase Join -- It could be outer join or inner join.

I am sure BO also supports this. Can someone confirm this.

1) Do we create 2 Universe and create another Univers.

2) Do we specifiy the Join condition or Union condition.

My terms may be in correct. Can you some please correct my terms and tell me how it is done in BO and what it is called.

Thanks a lot

Pankaj